It is well known that in analog display type watches display of the data is obtained in a classic manner by a disc or crown which bears on one of its surfaces the numbers from 1 to 31, said numbers running successively past an opening arranged in the dial of the timepiece. This indicator is driven in rotation by the gear train in a manner such that it progresses through one step every twenty-four hours. The blocking at each of the display positions of the date indicator is usually obtained by an elastic latching member successively engaging between the teeth arranged on the disc or crown as the indicator advances. During the daily actuation of such indicator, the driving force which must be applied thereto is thus clearly greater than the normal driving force necessary to drive the hands of the watch, since it is necessary to provide in addition the energy to cancel the effect of the elastic latching member.
The invention thus concerns the diminution of the couple necessary to be applied to the date indicator in order to have it make a step.
For instance, British Pat. No. 2 026 213 describes an elastic latching mechanism which is rendered inoperative during the date step in order to reduce the energy necessary during the advance. This mechanism comprises a driving train provided on its periphery with a toothed sector and a transmission train provided with first teeth adapted to mesh with the toothed sector of the driving train and second teeth in mesh with the teeth of the date indicator. A circular cam having a flattened sector is driven onto the axle of the driving train in a manner such that the flattened part is located facing the toothed sector. An elastic latching member formed with two branches is arranged in a manner such that the end of one branch bears on the cam and the end of the other branch comes into contact with the second teeth of the transmission train. The latching member may pivot about a point situated at the junction of the two branches the spread of which is dimensioned in a manner such that they are elastically urged against the cam and the second teeth when the date indicator is not being driven. The elastic support of one of the branches, provided moreover with embossing, assures the desired latching. At the moment that the data indicator makes the step, the flattened portion of the cam is brought into a position facing one branch and annuls the urging force of the other branch on the second teeth. The latching thus being rendered inoperative, the date indicator may be freely displaced. This latching mechanism presents however the difficulty that except for the times when the data is advanced, the cam which is permanently in rotation rubs on one branch, thus producing an undesirable energy loss.
To overcome the above-cited difficulty, the applicant of the present invention has already proposed an arrangement having no elastic latching arrangement such having been described in the Swiss Pat. No. 648 176 corresponding to U.S. Pat. No. 4,478,522 and which is related to mechanisms referred to as Maltese cross mechanisms, which permit driving in discontinuous rotation a driven train from a driving train turning at constant speed. In these mechanisms each actuation phase of the driven train is followed by a blocking phase of said mechanism in which it is unnecessary to employ spring indexing means. In the cited document, the blocking means applied employ a platen borne by the driving member and including a notch in the form of a half moon, said platen cooperating with a plate borne by the driven member and comprising four projecting arms at the extremity of which are fixed studs. This construction, in addition to requiring much space, necessitates special components not usually found in horology and relatively difficult to manufacture.
The purpose of the present invention is to provide an intermittent driving mechanism for a time indicator which avoids the above cited difficulties and which is simple to manufacture while remaining very secure in its operation. This purpose is attained thanks to the means set forth in the claims.